The present invention relates to a process for converting a gaseous feed material including an olefin mixture containing catalytic poisons such as water, oxides of carbon or sulfur-containing compounds, into higher molecular weight hydrocarbons including gasoline range products having aromatics present therein.
The conversion of olefins to aromatic compounds is not new in the art. In U.S. Pat. No. 4,238,318 by Kouwenhouven et al, C.sub.2 -C.sub.5 olefins or mixtures thereof were contacted with C.sub.1 -C.sub.5 paraffins at elevated temperatures with an aluminosilicate catalyst to produce an olefinic gasoline range mixture containing less than 20% by weight of aromatics. A two step process was utilized wherein the lower olefins were first oligmerized to olefins with a higher molecular weight and thereafter the higher olefins were then passed over the aluminosilica catalyst to yield the gasoline range compounds containing aromatics. In the first step of the process considerably milder conditions were applied than in the second aromaticizing step.
In U.S. Pat. No. 3,756,942 by Cattanach, a liquid feed material consisting essentially of paraffins, olefins, naphthenes, and mixtures thereof having a boiling point in the range from C.sub.5 and higher were converted to aromatics in the presence of a crystalline aluminosilicate catalyst of the ZSM-5 type.
In U.S. Pat. No. 3,760,024 by Cattanach, a feed consisting essentially of C.sub.2 -C.sub.4 paraffins and/or olefins was converted to aromatics in the presence of a crystalline aluminosilicate catalyst of the ZSM-5 type.
In a typical refinery operation, a significant amount of ethylene and propylene is utilized as fuel gas for refinery boiler operations. For example, the untreated off-gas from a fluidized catalytic cracker typically used as boiler feed is high in both ethylene and propylene along with contaminants such as oxides of carbon and hydrogen sulfide. In addition, the off-gas usually contains a significant amount of water up to the saturation point of the off-gas. It can be appreciated that these refinery streams would be much more valuable if converted to gasoline products than if used as boiler feed. Previously described processes provide methods to convert olefinic streams into useful aromatic products however, these processes utilize catalysts which undergo substantial degradation when exposed to water, oxides of carbon or sulfur-containing components. In particular, aluminosilicate catalysts of the ZSM-5 series have been reported to be unsuitable in the presence of water in that they rapidly lose activity when steam or water is present during the reaction. What is needed therefore is a process for converting these contaminated off-gas refinery streams containing ethylene and propylene into higher molecular weight hydrocarbons including useful gasoline range end products. What is also needed is a process utilizing a catalyst which is not deleteriously affected by the presence of these contaminants.
Recently, catalysts characterized as crystalline silica polymorphs prepared in accordance with specified procedures and known generically as silicalite type catalysts, have been discovered to be useful in these olefinic conversion processes. These catalysts are not subject to deactivation in the presence of water, oxides of carbon or sulfur-containing compounds.